1. Technical Field
This disclosure relates to suspension systems and, in particular, to suspension systems for trucks having tandem axles including a drive axle and a non-drive axle.
2. Discussion of Related Art
Vehicle suspension systems include a wide variety of configurations and structures. It is common in the large truck industry to provide dual or tandem axle configurations to support heavy loads. Often, a driven or powered axle is used in combination with a non-driven axle. In one configuration, the non-driven axle may be located rearward of the drive axle and is referred to as a “tag” axle. Alternatively, the non-drive axle may be located in front of the drive axle and is referred to as a “pusher” axle. Both tag and pusher non-drive axles can be non-steerable, power steerable or self-steering.
Tandem axle suspensions often include separate hanger brackets or other mounting devices for each of the two axles. It is also commonly known to connect the two axles with a pair of beams, commonly referred to as “suspension beams” or “walking beams,” and to pivotally connect the beams to the vehicle chassis with a single hanger bracket mounted to the beams between the two axles.
It has been found that when the single hanger bracket is located at or near the midpoint in the beams between the two axles, an inefficient application of downward force distributed equally to the driven and non-driven axle results. It has been determined that it is desirable and beneficial to place a greater load on the driven axle than on the non-driven axle, particularly in a self-steering tag axle configuration. In one common configuration, each suspension beam or walking beam is pivotally connected to the hanger bracket such that approximately 40% of the overall suspension beam length is located between the hanger pivot and the driven axle, and approximately 60% of the overall suspension beam length is located between the hanger pivot and the non-driven axle. This offset configuration, commonly referred to as a “60/40 tandem axle” or the like, is known to more efficiently distribute the load between the driven axle and the non-driven axle. The benefits of this configuration include improved traction, reduced tire scrub and reduced overall turning radius, when the tag is steerable.
In some cases, even with the 60/40 tandem axle distribution, traction control can be difficult. For example, in certain heavy trucks with non-drive tag axles, such as, for example, refuse trucks, it can be difficult to maintain traction. Specifically, when these trucks are empty, there may be insufficient downward force on the drive axle to ensure traction in unfavorable road conditions such as extreme grades with or without weather conditions such as rain, snow and the like.